KEYWORDS: Ion beams, Optical components, Ions, Chemical species, Thermal effects, Optical surfaces, Monte Carlo methods, Glasses, Sputter deposition, Optical simulations
Ion beam has the advantages of high accuracy and little damage to components, which has been widely used in the figuring of optical components. However, in figuring, the collision between the ions with high-speed collides and the surface of the optical component will cause the temperature of the optical component to rise quickly. In order to investigate the thermal effect of the ion beam figuring, the thermal deposition model is established based on the Sigmund theory of sputtering, and the thermal power density function of the surface heat source is obtained. On this basis, taking BK7 glass as the research object, Monte Carlo method was used to obtain the total power of thermal deposition under the different incidence angle of ion beam. Then the finite element method was used to simulate the thermal effect of the ion beam figuring. The result shows that the deposition energy, maximum temperature and the maximum stress decrease with the increase of incidence angle, and the maximum stress appeared in the clamping position of fixture. The corresponding simulation result shows that comparing with the fixing fixture, the maximum stress in the optical component could be reduced more than 70% by using elastic fixture.
o achieve the positioning and multi-degree-of-freedom machining of rotary micro-feature structures on the five- axis motion table in the focused ion beam micro-nano machining system, a high-precision sample rotator based on worm gear drive in vacuum environment is designed. The finite element method is used to simulate and optimize the key components. After loading, the maximum deformation of the component is less than 0.2μm, and the natural frequency is more than 10000Hz, which meet the requirements of the working accuracy and strength of the component. The focused ion beam machining experiment of high aspect ratio microstructure of metal material was carried out by using this sample rotator, and the surface roughness of metal material after machining was better than 5nm. The developed sample rotator expands the processing range of focused ion beam processing system.
During the optical components figuring by ion beam, the temperature of the optical component will rise quickly because of the collision between the ions and the atoms of the optical component. In order to investigate the thermal effect of the ion beam figuring, the thermal deposition model is established based on the Sigmund theory of sputtering, and the thermal power density function of the surface heat source is obtained. Moreover, the thermal power density function is also modified based on the geometric relationship between surface of optical component and ion beam for establishing the incidence of the angle of ion beam to thermal power density. On this basis, the CAE (Computer Aided Engineering method was used to simulate the progress of the BK7 glass figuring by ion beam. And the modified thermal power density function is programed as heat flow load in the CAE model. The total power of thermal deposition under the different incidence angle of ion beam was obtained by Monte Carlo method. The result shows that the modified thermal power density function is close to the experimental result in other literatures. Meanwhile, the result shows the deposition energy and the maximum stress decrease with the increase of incidence angle.
Double-sided rapid polishing machine is a new type of polishing equipment which utilizes the principle of chemical mechanical polishing and the shape precision copying mechanism to remove materials from the upper and lower surfaces of optical elements. To analyze the principle of double-sided rapid polishing machine, a material removal model based on Preston equation was established, and the relationship between the parameters such as eccentricity, rotational speed ratio and swing stroke and the material removal uniformity was obtained, which provided a theoretical basis for the double-sided rapid polishing process. With 430mm×430mm×10mm large diameter optical element as the experimental object, the double-sided rapid polishing test was carried out, and the precision index of surface shape accuracy λ/2 was obtained, which realized the high efficiency and high precision machining of plate optical element.
In order to the dwell time function can be solved quickly and accurately, the sampling step length of the dwell point in the solution process of ion beam polishing dwell time has been optimized. Taking the PV value for per unit of uniform material removal and dwell time as the analysis object, the fluctuation caused of uniform removal and the total dwell time under different dwell time sampling step length are analyzed. The optimal dwell time sampling step length of ion beam polishing is 1.5σ。Using the determined sampling step length, the optical element with a diameter of 50mm is simulated polishing, and the surface PV value of the element decreases from 110.81nm to 20.06 nm. The optical element was polished by ion beam according to the simulation results, the PV value of the element surface decreased from 110.81nm to 46.46nm. The experimental results verify the effectiveness of the simulation results. Using the determined dwell point sampling step length, the dwell time can be solved quickly, and the PV value of the optical elements converges well.
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